Ribbed plug type cap for plastic extrusion tube container



A. NICHOLS Oct. 25, 1955 RIBBED PLUG TYPE CAP FOR PLASTIC EXTRUSION TUBE CONTAINER Filed Nov. 19, 1955 W a W flTTUPNEYS United States Patent O RIBBED PLUG TYPE CAP FOR PLASTIC- EXTRUSION TUBE CONTAINER Anthony Nichols, North Piainfield, N. 1., assignor to Celluplastic Corporation, a corporation of New Jersey Application November 19, 1953, Serial No. 393,179

Claims. (Cl. 150-.5)

This invention relates to an improved type of cap for plastic extrusion tube containers.

The type of cap to which this invention relates is described in my copending application entitled Cap for Plastic Extrusion Tube Container, Serial No. 369,912, filed July 23, 1953. As set forth in that application, in order to achieve a cap which gives a satisfactory seal with plastic extrusion tube containers, the cap must be adapted to seal different size tubes because with present day equipment it is virtually impossible to produce an extrusion tube with predetermined diameter and wall thickness. In my first application I solve this problem and compensate for variations in wall thickness and tube diameter by providing the extrusion tube container With a plug type cap adapted to stretch the mouth of the tube a limited amount. Excessive stretching of the mouth of the tube is prevented by means of an annular flange positioned around the plug and as a result my cap gives a satisfactory seal regardless of variations in the dimensions of the tube.

I have now discovered thatit is possible to materially improve the seal of the cap of my first application by providing the plug with a series of longitudinal ribs for stretching and distorting the mouth of the tube. The ribs are positioned around the top portion of the plug and each rib has a cam surface at its lower end which tapers down to the surface of the plug. The portion of the plug below the ribs serves as a lead-in portion which is made small enough to start the plug into the mouth of the tube regardless of variations in tube diameter. When the cap is pushed home in the container the cam surface on the ribs cams and stretches the mouth of the tube up around the ribs which fit tightly into the tube and give exceptionally good sealing action. As in my first application, the cap has an annular flange which cooperates with the ribs to prevent excessive stretching of the mouth of the tube to a point Where it would give a loose fit.

My invention can be readily understood by reference to the accompanying drawing, in which V Fig. 1 is a front elevational view of my cap for a plastic extrusion tube container;

Fig. 2 is a sectional view taken on line 22 of Fig. 1;

Fig. 3 shows the cap of Fig. 1 in position in the mouth of a plastic extrusion tube container which is cut away in part to show construction of the tube;

Fig. 4A is an enlarged sectional view taken on line 4--4 of Fig. 3; and

Fig. 4B is similar to Fig. 4A but in this view the mouth of the tube is made larger than the plug of the cap.

The plastic extrusion tube container shown in Fig. 3 is made up of an ordinary plastic extrusion tube 12 having a bottom 14 which may be fixed in the tube in any convenient way, as for example, by means of an adhesive. The tube may be made of any suitable plastic material capable of extrusion molding such as the cellulose esters, cellulose ethers or highly plasticized vinyl derivatives and the like. I prefer to use cellulose acewith a tube one inch in diameter the thickness of the tube wall may vary about one thousandth of an inch or from approximately .013 to .012 inch. The outside diameter of the tube may vary about ten thousandths of an inch, or from approximately 1.060 to 1.070 inches. With a tube of such variable dimensions, the ordinary type of unthreaded cap which is made to fit a container of set dimensions does not give a satisfactory seal.

Referring to Fig. 1, cap 16 includes a top member 18 and a hollow thin-walled plug 20 having a series of Iongitudinal ribs 22 which protrude out from the surface of plug 20 and extend downwardly from top member 18 to a line at approximately the middle of the plug. At the lower end of each rib is a cam surface 24 which tapers down to the surface of the plug. Preferably the slope of cam surface 24 is abrupt and its length should not exceed approximately 2 /2 times the resulting increase in the diameter of the plug. That is, A should not exceed approximately 2 /2 B (see Fig. 2). In the drawings ribs 22 are shown with sharp edges for the purpose of clarity of illustration but these are not necessary and the edges of the ribs may be rounded off as may the surface of the ribs. The portion of plug 26 below ribs 22 serves as a lead-in portion which orients and guides the plug into the mouth of tube 12. If desired, the rim of plug 20 may be beveled as at 28 to assist in orienting the plug in the mouth of the tube.

The diameter of lead-in portion 26 is made slightly smaller than the minimum inside diameter of tube 12 and the eflective outside diameter of the plug as measured across a circle touching the outermost surfaces of ribs 22 is made slightly larger than the minimum inside diameter of tube 12. For example, if the extrusion tube has the dimensions described above I achieve a highly effective seal by making the diameter of lead-in portion 26 approximately 1.025 inches and the effective diameter of the plug as measured across a circle touching the outermost surfaces of ribs 22 (Fig. 4A) approximately 1.054 inches. With this construction the lead-in portion 26 readily fits into the mouth of tube 12 and when the cap is pushed home camming surfaces 24 stretch the mouth of the tube and guide it up on ribs 22. Excessive stretching of the mouth of tube 12 to a point where it would fit loosely on ribs 22 is prevented by an annular flange 30 which forms a slot 32 at the top of cap 16. For best results, I make slot 32 approximately .031 inch deep so that a seal is achieved between surface areas of ribs 22 and tube 12 and not just with the rim of the tube. By making the width of slot 32 between ribs 22 and flange 30 approximately .001 inch greater than the thickness of the walls of extrusion tube 12 the slot readily receives tube 12 and guides the open mouth of the tube along the surface of ribs 22. In the preferred form of my invention, however, I make the Width of slot 32 at ribs 22 approximately equal to the thickness of the wall of tube 12 or slightly smaller than the thickness of the wall. When this is done, ribs 22 and flange 30 grip on the inside and outside surfaces of the mouth of tube 12 to materially increase sealing action of the cap. If the space between ribs 22 and flange 30 in slot 32 is smaller than the thickness of the Wall of tube 12, cold flow of the plastic material in the Wall of tube 12 takes place as the cap is pushed home into the mouth of tube 12.

In some cases it is possible that control of extrusion molding may be temporarily upset and this may result in a tube having an inside diameter slightly greater than the effective outside diameter of the plug. In such case o thecap, tightlygrips thermouth of the tube in the space between ribs 22 and flange 32 and the excess material in the mouth of the tube is held in channels 34 between ribs 22. This situation is illustrated in Fig. 4B whic als illustrate l 'flow o pl ti m ial in the tube-wall caused;by having awall of greater thicknessthan-the width of thespace between ribs 22 and flange 30. As shown in Fig. 4B cold flow of the material,of;the tube enlarges thetube wall ;on each side of ribs 22 as at 36. Wherestandard tolerancesare maintained, stretching and distortionof the mouth of tube 12 by thecap isas shown in Fig. 4A. As there shown the 1 tube mouth is stretchedflat across channels 34. -Fig.-.4At.also ;illustrates, a.cap.in .which the .space betweent-ribs 22 and flange 50 is made approximately .001 inch greater thanthethickness ofthetube wall.

,Anoth er,advantage ofusingvribs 22 for stretchingthe mouthoftube, 12; is that thecap,always fits tightly into the tube'anddoes not lose, its sealing action, during use. Upon nitial closingof the container, each rib is impressed into the wallof the tube ina certain position and,each timethe container is closedthereafterthe ribs oqcupy;,a slightly di fferent,position so thatthe mouth of; the-tube is stretched and. distortedueach time the container is closed. As -a.result, the .cap always .gives a tight fit with the tube.

Forrbest results, the dimensions, of cap116 should be closely controlled. This-may readily be doneby forming cap 16 by means of any of the well-known methods of molding .such as injection molding. Since the standard tolerance of such a molded piece is plus or minus 005, the maximumdiameter of lead-in portion 26;for-the example given above would-be 1.030 inches whichis .004 less than the minimum inside diameter (1.034 inches) of extrusion tube 12. Similarlythe effective minimum outside diameter. of plug as measured-across a circle around the plug touching the. outermostzsurfaces of ribs '22 would be 1.049 inches which is .003 more. than the maximum. outside. diameter (1.046 inches) oftube 12.

Since the cap=stretehes the mouth of tube 12 it must have a greater resistance to distortion than the materiaL of the tube. For example, when the cap is made byvinjection molding, I may usepolystyrene or one of the vacetate'materials. or if-the cap is madeby compression molding I may use the phenolic or urea plastic materials. For best results I use apolystyrene cap for a.tube of cellulose-acetate and I prefer to keep the difference in hardness .and resistance to distortion of the materials of the cap andtube equivalent to the difference in hardness between polystyrene and cellulose acetate.

.ltiwill beunderstood that:I do not intend to limit my invention to theexample given herein which is merely.--chosen for the purpose ofillustration. It will be further understood that it is intended to cover all changes and modifications of-my invention which do not constitute departures fromthe-spirit andscope of the invention.

WhatiI claim is:

l. A cap-adapted to seal the mouth of an extrusion tubecontainer, :said cap comprising a plug of plastic materialadaptedgto fit into the open mouth of the container said plug having ribs positioned on and around the exterior surface thereof, said ribs extending downwardly from :the-top ,of the plug and terminating in cam;,surfaces-tapering down to:the exterior surfaceof the plug, said plug and ribs'having an efiectiveoutside diameteras measured acrossa circle around the plug touching the outermost surface of the ribs which is slightly greater than the minimum inside diameter of the container, whereby the mouth of the tube is stretched as it rides up over the cam surfaces of the ribs to form a frictional surface fit with the ribs when the cap is pushed home into the mouth of the container, and said plug having a top member which extends outwardly over the rim of the container.

2. A structure as specified in claim 1 in which the top member includes an annular flange spaced outwardly away from the plug to form a slot around the plug and ribs for receiving the mouth of the container.

3. A structure as specified in claim 1 in which the cam surfacesof the ribs terminatein the surface of the plug at a substantialdistance above the bottom of the plug to provide a lead-in portion for guiding the container up on the ribs of the cap, said lead-in portion being of smaller outside diameter than the inside diametem h o aine 4. A cap for an extrusion tube containerwhicheomprises ,a plug of plastic-material.adapted to fitinto the open mouth ofthe container, said plughaving; ribspositioned on and around the exterior surface thereof, said ribs-extending downwardly from the top of the plug and terminating-idcam surfaces tapering down to the exteriorsurfaee-of theplug, said plug having a top member which-extends outwardly over the-rim of the container and an annular flange affixed to such top member-spaced outwardly away from the ribs of the plug to form a slot between the exterior surface of the ribs and; interior; surface of the flange for receiving the mouth of the container, said slot being approximately equal to the thickness of the wallof said container at the mouth of the tube whereby the mouth of the tube is tightly gripped on both its inside and outside surfaces by the ribs and annular flange respectively when the container mouth is pushed home in the slot of the cap to seal the tube.

5. A cap for a plastic extrusion tube container which comprises a plug of ,plastic material having a series of ribs positioned around the top portion of the plug on the exterior surface thereof which extend downwardly along the exterior surface ,of the plug and terminate at-their lowerend in a cam surface tapering down to the exterionsurface of theplug, a cover member positioned across the top of said plug which extends outwardly beyond the rim of the plug, an annular flange aflixed tosaid-cover member which extends downwardly from the. cover member and which is spaced outwardly away from ,the surface of the top portion of the plug to form vaslot betweenthe exterior surface of the ribs and interior surface of the flange for receiving the mouth of thecontainer, saidslot being approximately equal to the thickness of the wall of said container at the mouth of the tube whereby the mouth of the tube is tightly gripped on both its inside and outside surfaces by the ribs and annular flange, respectively, when the container mouth is pushed home in the slot of the cap to seal thetube.

References Cited in the file of this patent UNITED STATES PATENTS 2,487,400 Tupper Nov. 8, 1949 2,526,225 Gronemeyer Oct. 17, 1950 2,606,586 Hill Aug. 12, 1952 2,675,040 Raun et al Apr. 13, 1954 

